JP3747207B2 - Light unit for display - Google Patents

Description

  The present invention relates to a display light unit used for a backlight such as an LCD panel, and more particularly to a display light unit configured to emit light incident from the side in a vertical direction.

  Recently, liquid crystal display (LCD) devices have been widely adopted in personal computer monitors, flat-screen TVs, mobile phones, and the like. The liquid crystal display device does not have a self-luminous capability and requires a separate illumination device. Therefore, the liquid crystal display device is provided with a planar illumination device, that is, a backlight (surface light source device). The backlight has a structure in which a linear light source such as a cold cathode discharge tube is converted into planar light.

  Specifically, the light unit is configured by providing a light source below the rear surface of the liquid crystal element, or by providing a light source on the side surface and using a translucent light guide such as an acrylic plate to convert the light into a surface shape. Examples thereof include a method of obtaining a surface light source (side light method) and a method of obtaining desired optical characteristics by providing an optical element composed of a prism array or the like on the light emitting surface.

  Among the above methods, as a method of using a light guide by providing a light source on the side surface, there is a method of using a prism sheet 15 as shown in FIG. FIG. 1 is a view showing a conventional light unit using a prism sheet.

  In FIG. 1, the white light source 10 is positioned on the side surface of the light guide plate 13, the reflection plate 11 is positioned below the light guide plate, and the diffusion plate 14, the prism sheet 15, and the protection sheet 16 are positioned above the light guide plate 13. It is arranged. The LCD panel 17 is positioned above the protective sheet 16. Under the light guide plate 13, a scattering pattern is formed such that a dot pattern is printed or a printless pattern 18 such as a V-shaped groove is formed.

  The operation of such a light unit will be described. First, incident light emitted from the white light source 10 is incident on the light guide plate 13. After the light enters the light guide plate 13, light having an angle smaller than the total reflection angle is emitted by the scattering pattern and sent to the diffusion sheet 14. The diffusion sheet 14 transmits light to the prism sheet 15 with uniform luminance, and the prism sheet collects light on the front surface and emits it.

  The white light source 10 is a multi-wavelength light source, and each wavelength (Red, Green, Blue) light incident on the light guide plate is diffracted by the diffraction pattern 19 formed on the light guide plate and emitted from the light guide plate. The diffraction angle is different. Due to the difference in the diffraction angle for each wavelength, the light emitted to the front surface is dispersed, and there is a problem that white surface light cannot be generated. This is shown in FIG. That is, the emission angles from which R, G, and B light are emitted do not coincide with each other.

  Accordingly, in the light unit shown in FIG. 1, a diffuser 14 is used. The diffusion plate is used to increase the uniformity of light and generate uniform surface light, and is formed so that the film surface is randomly processed to scatter light. The diffusing plate 14 diffuses the light incident on the diffusing plate and reduces the separation by wavelength of the emitted light.

  However, the diffusing plate 14 acts so as to scatter light and overlap light of each wavelength in this way, and cannot fundamentally overcome the color separation phenomenon due to the difference in wavelength. Further, the light unit of FIG. 1 has a disadvantage that the structure becomes complicated because a plurality of prism sheets and a diffusion plate are used.

  FIG. 3 is a diagram showing a conventional light unit using a hologram pattern. In FIG. 3, the light emitted from the light source 20 located on the side surface enters the light guide plate 21. A hologram diffraction pattern 22 is formed on the light guide plate 21 so that light is emitted from the light guide plate 21 to the front at an angle of approximately 90 degrees.

  Even in a light unit that does not use a conventional prism sheet as shown in FIG. 3, color separation as shown in FIG. 2 occurs. That is, the light emitted from the light guide plate to the front is diffracted by the hologram diffraction pattern formed on the upper portion of the light guide plate. At this time, a phenomenon occurs in which the colors of the emitted light appear to be dispersed with different diffraction angles for each wavelength.

  Therefore, the light unit using the hologram diffraction pattern as shown in FIG. 3 needs the pattern design as shown in FIG. FIG. 4 shows the pattern formation surface of the light guide plate, and the diffraction pattern is formed differently according to each wavelength of light emitted from the light guide plate. That is, the area of the pattern formation surface is divided, and the area where the R wavelength is emitted at 90 degrees and the area where the G and B wavelength lights are emitted at 90 degrees are divided. In this case, only the wavelength selected in each wavelength region is emitted at an angle of about 90 degrees, and these regions are continuously arranged so that the user does not feel color separation.

  However, continuously arranging different patterns on the light guide plate as described above has a problem that the process is complicated and the productivity is poor. Also, such a hologram pattern arrangement is not a more fundamental solution for color separation.

The present invention has been devised to solve the above-mentioned problems, and a color separation prevention plate is provided at the lower part of the light guide plate, so that when the multi-wavelength light incident from the side is emitted to the front, It is an object to provide a light unit that prevents color separation caused by different diffraction angles.
Furthermore, an object of the present invention is to provide a backlight unit for an LCD panel that provides improved surface light as compared with the prior art.

  Furthermore, the present invention eliminates the need for using an optical component such as a conventional diffuser to change the light path, and provides a light unit that is thinner than the conventional light unit, thereby reducing the size of the product. Has a purpose.

  As a configuration means for achieving the above-described object, the present invention provides a light source that emits multi-wavelength white light; a light guide plate that is located on the side of the light source and causes incident light from the light source to travel inside; A color separation plate that is located on the opposite surface of the front surface of the light guide plate and refracts light in the light guide plate at different angles for each wavelength and travels in the light guide plate; and in the front surface or rear surface of the light guide plate A display light unit including a diffraction pattern formed on at least one surface and configured to emit light having the same emission angle through the color separation plate traveling at different angles for each wavelength.

  Preferably, the color separation plate has an inclined surface that allows the light traveling in the light guide plate to have an incident angle α satisfying the following formula.

sinα = −mλ / nd
here,
α: Angle formed by light in the light guide plate and the normal of the exit surface (incident angle)
m: Order (..., -1, 0, 1, 2, 3, ...)
λ: wavelength
d: Pitch of diffraction pattern of light guide plate
n: Refractive index of light guide plate

  Preferably, a cross section of the color separation plate is a triangle repeated at a constant pitch, and a pitch of the color separation plate is in a range of 0.5 mm to 2.0 mm.

  Preferably, the light enters and exits the color separation plate on the same surface of the color separation plate or on different surfaces.

  Preferably, the diffraction pattern is a hologram diffraction pattern obtained from a hologram exposure step, and is positioned between the light source and the light guide plate, and a light path incident on the light guide plate is from a horizontal plane with respect to the light guide plate. A path correction member that is inclined at a predetermined angle may be additionally included.

  Preferably, the color separation plate has a refractive index n of 1.0 <n <1.8, and the color separation plate can be formed of a transparent resin material.

  Preferably, the color separation plate is formed of an optical medium having a flint refractive index.

  As described above, according to the present invention, the color separation plate is provided at the lower part of the light guide plate, and when the multi-wavelength light incident from the side surface is emitted to the front, it is possible to prevent color separation caused by different diffraction angles for each wavelength of light. it can.

  In addition, the present invention can provide a backlight unit for an LCD panel that prevents color separation and provides improved surface light compared to the prior art, and uses conventional optical components such as diffusers. Therefore, it is possible to reduce the size of the product by providing a light unit having a thickness smaller than that of a conventional light unit.

  Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. The present invention includes a light guide plate, a light source located on the side surface of the light guide plate, a color separation plate located on the lower surface of the light guide plate, and a diffraction pattern formed on the upper surface of the light guide plate. FIG. 5 is a cross-sectional view of a display light unit according to the present invention.

[light source]
As shown in FIG. 5, the light unit according to the present invention includes a light guide plate 120 formed of a light transmissive flat plate. A light source 110 that emits multi-wavelength white light is disposed on one side of the light guide plate 120. The light source 110 has a linear shape and a fluorescent tube or an LED array is used, but is not limited thereto. In particular, the light source may be a cold cathode tube having excellent luminous efficiency and capable of being downsized.

[Light guide plate]
A light guide plate 120 is located on the side of the light source 110. The light guide plate 120 has a front surface 120a and a rear surface 120b, and includes an incident side surface 120c between the front surface and the rear surface. The front surface 120a is a surface on the observer side, and the rear surface is a surface on the opposite side to the observer. Further, the light source 110 is provided adjacent to the incident side surface 120c.

  The light guide plate 120 is a rectangular light-transmitting thin plate, and can be formed of an appropriate material exhibiting transparency according to the wavelength range of the light source. Examples of substances used in the visible light region include a transparent resin and glass, and the transparent resin includes an acrylic resin, a polycarbonate resin, or an epoxy resin. The light guide plate 120 can be formed by cutting or the like.

  A diffraction pattern is formed on the front surface 120 a of the light guide plate 120. This fulfills the function of emitting incident light 102 in a direction substantially perpendicular to the front surface (or emission surface, 120a) of the light guide plate.

[Diffraction pattern]
The diffraction pattern is formed on the front surface or the rear surface of the light guide plate 120. The diffraction pattern formed on the light guide plate 120 is preferably a hologram pattern obtained by a hologram exposure process. The hologram pattern is one of diffraction patterns that perform the function of diffracting light. If the hologram diffraction pattern is used, the passing light can be adjusted to have a desired angle. This is different from the case where a normal diffraction grating is composed of slits, and all of the slits are allowed to pass through and are completely blocked. The shape and pitch of the hologram diffraction pattern can be arbitrarily adjusted to obtain a desired diffraction angle according to the wavelength of the incident light. The relationship between the pitch of the hologram diffraction pattern and the incident light will be described later.

  The hologram diffraction grating is obtained by drawing a number of parallel lines at equal intervals on a flat glass or a concave metal plate. When irradiated with light, the transmitted or reflected light is divided according to wavelength, and its spectrum is obtained. Light incident in parallel to the diffraction grating (formed from the flat glass) is absorbed or scattered at the point where the line is drawn, and light entering from a narrow gap where no line is drawn is allowed to pass. However, the light that has passed does not travel straight, but is diffracted and diffused in a cylindrical shape by the Hoyens principle.

  Holograms are classified into a reflection type and a transmission type depending on the reproduction method. In the transmission hologram, an image transmitted through the hologram by applying light from the back of the hologram during reproduction is observed in front of the hologram. This is a method of projecting forward through a reflector located behind the hologram pattern as in the present invention. On the other hand, the reflection type hologram is produced such that an image reflected from the hologram by irradiating light before the hologram during reproduction is observed in front of the hologram.

  In order to produce a conventional diffraction grating on the light guide plate, conventionally, a method of vacuum-depositing aluminum on a glass plate processed with high precision and drawing a line by a mechanical method using diamond is used. At this time, there is a problem that the production time is very long and the lines are easily bent when the lines are drawn, and the distance between the lines is not constant.

  On the other hand, in the case of a diffraction grating manufactured by a holographic method, it is easy to manufacture, the grating interval can be made constant and extremely narrow, and a resolution of 10,000 lines / mm can be obtained depending on the type of photosensitive material.

  In order to obtain the diffraction pattern as described above, a hologram exposure method as shown in FIG. 13 can be used. In this method, the photoresist was exposed to light using the coherence of the laser beam, and then developed to develop a stamper for mass production. That is, as shown in FIG. 12, the light emitted from the laser 310 passes through the beam diffuser 312 and passes through the XY drive drives 314 and 316 for pattern sequential exposure. Such light is branched through a beam splitter (B / S) 318. The branched light is divided into reference light and object light, which are generally called holograms, and travels, and a path difference is given to the light by a reflecting mirror 320 or the like to generate a phase difference between both beams. The special filter including the object lens 322 and the pinhole 324 eliminates light noise and the like so that uniform diffused light can be obtained. Such light is exposed to the glass plate 330 on which the photoresist is uniformly applied. Here, the pitch of the diffraction pattern depends on the coherence due to the phase difference between the two lights, but is adjusted by the difference in the incident angles of the two lights, and the depth of the pattern depends on the exposure of the specific wavelength and the degree of reaction of the photosensitive material. It is adjustable.

[Color separation board]
The color dispersion sheet 130 is positioned in contact with the rear surface 120b of the light guide plate 120. The color separation plate 130 refracts the light in the light guide plate 120 at different angles for each wavelength and advances the light in the light guide plate. The color separation plate is made of a translucent material, and includes glass, transparent synthetic resin, and the like.

  The color separation plate may be formed of an optical medium having a flint refractive index. The flint system is a material having a high refractive index, a small dispersion constant, and frequent dispersion. Therefore, in order to generate more color separation, it can be said that it is preferable to use a flint material.

  The refractive index of the color separation plate 130 is determined by the incident angle to the color separation plate and the shape of the color separation plate, and in particular, a material having a small difference in refractive index compared with the incident medium and a large color dispersion is selected. Become. At this time, the range of the refractive index (n) is preferably 1.0 <n <1.8.

  The color separation plate 130 has a shape in which triangular sections are repeatedly arranged as shown in FIG. That is, a plurality of convex portions having a triangular cross section having a predetermined pitch as shown in FIGS. 10 and 11 are formed. In this case, FIG. 10 shows the case where the surface that meets the incident light incident on the color separation plate is an inclined surface, and FIG. 11 shows the case where the surface that meets the incident light incident on the color separation plate is a vertical surface. Below, it demonstrates centering on the color separation board of FIG.

[Color separation plate-path]
In FIG. 6, light 102 is incident on the inclined surface of the color separation plate. The light 102 is the same as the light that enters the light guide plate 120 from the light source 110 and travels within the light guide plate to enter the color separation plate. At this time, the light incident on the color separation plate is multi-wavelength light, and light of each wavelength, that is, red (red, R), blue (blue, B), and green (green, G) light is the same. Incident at an incident angle.

  When each wavelength light incident on the color separation plate is refracted while forming a different refraction angle for each wavelength in the color separation plate, and is again emitted to the outside of the color separation plate and put into the light guide plate, The difference in the output angle for each wavelength increases.

[Color separation plate-refraction]
FIG. 7 is a diagram showing in detail the light path in the color separation plate of FIG. In FIG. 7, light traveling in the light guide plate enters (A). At this time, the incident angle is θ ₁ . The incident light is advanced and refracted by the color separation plate within 130 (B), the angle refracted at this time and theta _2. The light refracted again is reflected on the bottom surface of the color separation plate (C), and the angles of reflection and advance are θ ₃ and θ ₄ . The light that has passed through the C path is emitted again from the color separation plate. At this time, the angle of incidence on the boundary surface of the color separation plate is θ _5, and the angle of emission is θ ₆ .

  On the other hand, the incident angle that enters the diffraction pattern on the upper part of the light guide plate through the light guide plate through the color separation plate is α, and the angle that the inclined surface of the color separation plate forms with the horizontal plane is β.

  Consider the relationship between the angles.

  First, the incident angle and outgoing angle of light traveling to another medium having a different refractive index satisfy the following equations.

n ₁₂ = sin θ _t / sin θ _i (1)
n ₁ : refractive index of the incident side medium
n ₂ : refractive index of the exit side medium θ _t : exit angle θ _i : incident angle

Light entering through the A path enters at an angle of θ ₁ and exits into the color separation plate at an angle of θ ₂ . At this time, if the refractive index of air on the A path is 1 (n ₁ = 1) and the refractive index of the color separation plate is n (n ₂ = n), the following equation is satisfied (Snell's Law).

From n ₁ sinθ ₁ = n ₂ sinθ ₂
sinθ ₁ = nsinθ ₂ (2)

  The relationship between the angles in consideration of geometric conditions in the color separation plate is as follows.

θ ₅ = θ ₂ + 2β Equation (3)
α = θ ₆ −β (4)

  Again, the exit angle of light exiting the color separation plate through the D path satisfies the following equation.

sinθ ₆ = nsinθ ₅ (5)

Relational expressions of α, β, and θ ₁ can be obtained from the equations (2) to (5).

α = sin ⁻¹ [nsin [sin ⁻¹ [(1 / n) sin θ ₁ ] + 2β]] − β (6)

When the angle of incidence (θ ₁ ) incident on the color separation plate is determined from the above formula, the angle of incidence (β) of the inclined surface of the color separation plate is adjusted to determine the angle of incidence on the diffraction pattern of the light guide plate ( α) can be determined.

  As described above, the light entering the light guide plate again through the color separation plate is separated for each wavelength and enters at different angles. That is, in the above formula (6), the refractive index differs depending on each wavelength, and the output angle differs by about 10 degrees centering on the G wavelength light.

  The present invention is characterized by utilizing the separation phenomenon due to the refractive index of light in the color separation plate as described above, and thus the light emitted from the color separation plate is separated according to wavelength and proceeds to the light guide plate. .

[Diffraction of light by wavelength]
On the other hand, the incident angle of light incident on the diffraction pattern of the light guide plate and the exit angle of light exiting through the diffraction pattern have the following relationship (see FIG. 8).

P = mλ / (sinθ _t −sinα) (7)
here,
P: Pattern pitch
m: Diffraction order λ: Wavelength θ _t : Output angle θ _i : Incident angle

  Light entering the color separation plate enters through the air layer from the light guide plate, and then exits into the air again from the color separation plate. At this time, the difference between the refractive index of the light guide plate and the refractive index of the adjacent medium. It can be seen from the above formula that the smaller the is, the wider the range of the incident angle separation angle.

  Therefore, the following formula must be satisfied so that the output angle of the incident light can be substantially 0 degrees, that is, the pitch P of the grating from which the light exits from the exit surface of the light guide plate in the vertical direction can be produced.

  P = mλ / (− sinα) (8)

  In the equation (8), the incident angle α to the diffraction pattern is determined by the equation (6). At this time, the incident angle α varies depending on each wavelength (λ).

  Therefore, as in the equations (6) and (8), the incident angle at which each wavelength-specific light enters the diffraction pattern of the light guide plate is determined according to the inclination angle β of the inclined surface of the color separation plate. The pitch P of the diffraction pattern can be determined according to the incident angle α and the wavelength.

  Due to the pitch of the diffraction pattern determined from the above process, light is emitted from the light guide plate in a substantially vertical direction over all wavelengths.

  The above results are derived on the assumption that a hologram pattern is formed on the rear surface of the light guide plate. At this time, light is emitted from the color separation plate into the air, and again the hologram pattern below the light guide plate. Diffracts when incident on

  On the other hand, when a hologram pattern is formed on the upper surface of the light guide plate, it is necessary to consider refraction when light emitted into the air through the color separation plate enters the light guide plate again. As described above, Snell's law can be applied to the refraction at this time, and the incident angle of light traveling inside the light guide plate to the upper surface of the light guide plate can be obtained by the refractive index of the light guide plate and air.

[Example]
In the following, the pitch of the hologram diffraction grating is determined in the light unit according to the present invention, and the accompanying color separation reduction effect will be described.

  Table 1 shows the relationship between the incident angle and inclination angle of the color separation plate and the incident angle to the diffraction pattern.

  The results in Table 1 show that when the pitch of the hologram diffraction pattern on the light guide plate is 0.45 μm, the incident angle α of the diffraction pattern is not 55 °, and the distribution of light emitted to the front is in the optimum condition. In this case, when the angle β of the inclined surface of the color separation plate is set to about 12 °, an optimum light distribution can be obtained. In this case, the incident angle of the light incident on the color separation plate is in the range of 15 to 25 °, and the light in such a range can be appropriately separated.

  Table 2 below shows the actually calculated refractive index and incident angle α of other wavelength light under the above conditions. When the refractive index difference between the air and the color separation plate is 0.04 as shown in Table 2, the separation angle of the wavelength-dependent light emitted from the color separation plate is about 3 degrees.

[shape]
FIG. 10 is a perspective view showing an embodiment of the color separation plate of the light unit according to the present invention. The shape of the color separation plate 130 as described above is shown in FIG. According to FIG. 10, the light incident surface is inclined, and the distance between the inclined surfaces, that is, the pitch is in the range of 0.5 mm to 2.0 mm. At this time, the maximum height of the convex portion having the triangular cross-sectional shape is formed in a range of 0.1 mm to 0.5 mm.

  Here, the pitch range is set to 0.5 mm or more. If the pitch range is smaller than 0.5 mm, the convex portion of the triangular color separation plate is thin, and the traveling path of light in the color separation plate is shortened. This is because the color dispersion effect is reduced. On the other hand, if it is larger than 2.0 mm, the thickness of the color separation plate becomes too thick, causing a problem of increasing the thickness of the light unit as a whole. Therefore, it is preferable to form the pitch in the above range.

  The light traveling path in the color separation plate having the shape as shown in FIG. 10 is the same as that described above. Such a color separation plate is characterized in that the light incident surface and the light emitting surface are the same. That is, incidence and emission are performed through the same surface.

  On the other hand, FIG. 11 shows a color separation plate 135 having a shape in which light incidence and emission are performed on different surfaces. Similarly to the color separation plate of FIG. 10, the color separation plate of FIG. 11 has a convex portion having a triangular cross section, and the pitch and depth thereof are also selected for the same reason as in FIG.

  However, in the case of the color separation plate of FIG. 11, the incident surface on which light is incident is a vertical surface, and the surface from which light is emitted is an inclined inclined surface. That is, the light incident surface and the light exit surface are different.

  FIG. 12 shows a light path in the color separation plate having such a shape. As shown in FIG. 12, the light 102 is incident on the vertical plane at a predetermined angle from the horizontal plane, refracted in the color separation plate, reflected at the bottom, and emitted again from the inclined surface of the color separation plate and incident on the light guide plate. At this time, the color separation effect as described above is generated, whereby the light enters the diffraction pattern of the light guide plate at different angles for each wavelength and exits in a substantially vertical state.

  The color separation plate in which the vertical plane is formed so as to form a path as shown in FIG. 12 has a configuration in which the efficiency of light incident on the color separation plate is further increased. That is, since the light is positioned on the side of the light guide plate, the light path travels almost horizontally. As a result, a large amount of light enters the color separation plate.

[Path correction member]
In the light unit according to the present invention, preferably, a path correction member 150 can be provided between the light source 110 and the light guide plate 120 as shown in FIG. The path correction member 150 has a function of correcting the path of light coming out horizontally from the light source so as to be inclined toward the color separation plate 130. For this purpose, the light source 110 side surface is formed vertically and the light guide plate side surface is inclined. The path correction member can be formed of the same translucent material as the light guide plate, and the refractive index and shape of the correction member are determined in consideration of the design shape of the color separation plate.

  When the light path is adjusted using such a path correction member, the light input to the color separation plate 130 as shown in FIG. 10 is incident in a substantially vertical state, and the density of the incident light can be increased. . Accordingly, the light can be refracted in a larger amount and color-separated for each wavelength, and the amount of light for each wavelength subjected to color separation can be further increased.

  While the invention has been illustrated and described with reference to specific embodiments, it will be appreciated by those skilled in the art that the invention can be modified and varied in many ways without departing from the spirit and scope of the invention as defined by the following claims. It is clear that anyone with ordinary knowledge can easily come up with it.

It is a figure which shows the conventional light unit using a prism sheet. It is a figure which shows color separation of the light radiate | emitted from a light-guide plate. It is a figure which shows the conventional light unit using a hologram pattern. It is a figure which shows the formation surface of the hologram pattern used for the light unit of FIG. It is sectional drawing of the light unit for a display by this invention. It is sectional drawing of the color separation board used for FIG. It is a figure which shows the path | route of the light in the color separation board of FIG. It is a figure which shows the vertical emission of the light from a light-guide plate. 7 is a graph showing a distribution of emission angles depending on the angle of light incident on the color separation plate of FIG. 6. FIG. 3 is a perspective view illustrating an example of a color separation plate of a light unit according to the present invention. It is a perspective view which shows the modification Example of the color separation plate of the light unit by this invention. It is a figure which shows the light path of the color separation board of the light unit of FIG. It is a figure which shows one example of a manufacturing process of the diffraction pattern formed in the light-guide plate of the light unit by this invention. It is a figure which shows the installation state of the optical path correction member used for the light unit by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 110 ... Light source 120 ... Light guide plate 130 ... Color separation plate 150 ... Path | route correction member

Claims (9)

A light source that emits multi-wavelength white light;
A light guide plate which is located on the side of the light source and allows the incident light from the light source to travel inside;
A color separation plate that is located on the opposite surface of the front surface of the light guide plate and refracts light in the light guide plate at different angles for each wavelength and travels in the light guide plate; and
A diffraction pattern formed on at least one of the front surface and the rear surface of the light guide plate and configured to emit light having the same emission angle through the color separation plate traveling at different angles for each wavelength;
Only including,
The color separation plate has an inclined surface that is repeated at a pitch in a range of 0.5 mm to 2.0 mm, and the inclined surface has an incident angle α that allows light traveling in the light guide plate to satisfy the following formula: Display light unit characterized by:
sinα = −mλ / nd
here,
α: Angle formed by light in the light guide plate and the normal of the exit surface (incident angle)
m: Order (..., -1, 0, 1, 2, 3, ...)
λ: wavelength
d: Pitch of diffraction pattern of light guide plate
n: Refractive index of the light guide plate. The display light unit according to claim 1 , wherein a cross section of the color separation plate is a triangle repeated at a constant pitch.   2. The display light unit according to claim 1, wherein light is incident on and emitted from the color separation plate on the same surface of the color separation plate. 3.   2. The display light unit according to claim 1, wherein light is incident on and emitted from the color separation plate on different surfaces of the color separation plate. 3.   2. The display light unit according to claim 1, wherein the diffraction pattern is a hologram diffraction pattern obtained from a hologram exposure step.   2. The apparatus according to claim 1, further comprising a path correction member positioned between the light source and the light guide plate and tilting a path of light incident on the light guide plate at a predetermined angle from a horizontal plane with the light guide plate. The light unit for display as described.   2. The display light unit according to claim 1, wherein a refractive index n of the color separation plate satisfies 1.0 <n <1.8.   The light unit for display according to claim 1, wherein the color separation plate is made of a transparent resin material.   2. The display light unit according to claim 1, wherein the color separation plate is formed of an optical medium having a flint refractive index.

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